Liquid crystal display device utilizing in-plane-switching system and having alignment film separating picture element electrode or counter electrode from liquid crystal layer

ABSTRACT

A liquid crystal display device includes a pair of substrates, a liquid crystal layer supported between the pair of substrates, a plurality of gate electric wirings provided on one of the pair of substrates, a plurality of drain electric wirings respectively intersecting with the plurality of gate electric wirings in a matrix configuration, a plurality of thin film transistors formed on respective points of the gate electric wirings and the drain electric wirings, a plurality of common electric wirings extending in the same direction as the gate electric wirings, a plurality of picture elements with at least one of the picture elements being respectively surrounded by the gate electric wirings and the drain electric wirings, and a plurality of counter electrodes connected to the common electric wirings and extending in the same direction as the drain electric wirings. A plurality of picture element electrodes made of at least one of conductive oxide and graphite are connected to the thin film transistors and extend in the same direction as the drain electric wirings. An electric field having a component parallel to one of the pair of substrates is produced in the liquid crystal layer by an electric voltage applied between the counter electrodes and the picture element electrodes, and the respective picture element electrodes are in contact with the liquid crystal layer directly or through an alignment film.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 08/906,475, filedAug. 5, 1997, now U.S. Pat. No. 5,995,187 the subject matter of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to a liquid crystal display device fordriving a liquid crystal by means of an in-plane-switching system toapply an electric field which is almost parallel to a substrate betweena picture element electrode and counter electrode.

An active matrix type liquid crystal display device using an activecomponent, such as a thin film transistor (TFT), is widely used as adisplay, having such characteristics as being thin and light weight, andhaving a high displaying quality. A liquid crystal display device ofthis type is constructed with a liquid crystal provided between anactive matrix substrate having a TFT element and an opposite substrate,and an electric field is applied between picture element electrodes anda counter electrode so as to drive and control the liquid crystal,whereby light incident on the liquid crystal is modulated so as to forman image.

Further, in order to widen the viewing angle of a liquid crystal displaydevice, a liquid crystal display device using an in-plane-switchingsystem has been proposed, in which the picture element electrode and thecounter electrode are formed on the active matrix substrate, and anelectric field is applied in parallel to the surface of the substrate.Such a device is described, for example, in Proceedings of the 15thInternational Display Research Conference, p. 707 (1995) or JapanesePatent Laid-open 7-36058 Bretin. The in-plane-switching system has theadvantage of being able to provide a wide visual angle, because theliquid crystal is controlled by an electric field applied in asubstantially transverse direction relative to the viewing angle.

The conventional display device using in-plane-switching has aconfiguration in which metal films, formed under a protective insulationfilm, serve as the picture element electrodes and the counter electrodesthereto. However, since the electric field is applied to the liquidcrystal through the protective insulation film, an electrical voltageloss occurs, with the result that the driving voltage becomes large,causing a problem in that the power consumption increases. Moreover,while it is effective to make the spacing between the picture elementelectrodes and the counter electrodes big in order to enlarge theaperture ratio, this requires the driving voltage to be even larger.Since the threshold driving voltage of the liquid crystal is restrictedby the upper limit of the driving voltage, there arises a problem inthat the selection of a liquid crystal which has a fast responsivenessis limited.

Such an increase in the power consumption caused by such an electricalvoltage loss may be avoided by providing a contact hole which forms anaperture in the gating isolation film and by providing an electrode fordriving the liquid crystal through this aperture, as described inJapanese Patent Laid-open No. issue 7-128683 bulletin. However, theusual metal electrode has a problem in that it is corroded by the liquidcrystal composition, so that it is necessary to form a protectiveinsulation film on top of the electrodes. Naturally, in this case, theelectrical voltage loss which occurs due to the protective insulationfilm increases even more.

SUMMARY OF THE INVENTION

An object of the present invention is to reduce losses in the drivingvoltage applied to the liquid crystal, by providing an active matrixsubstrate in which degradation of the metal electrode is prevented in aliquid crystal display device.

In the liquid crystal display device of the present invention, pluralgate electric wiring, plural drain electric wiring intersectingtherewith in a matrix state, plural thin film transistors formedopposite to each intersection of the gate and drain electric wiring, andplural common electric wiring extending in the same direction as thegate electric wiring are provided on one of a pair of substrates. Atleast one picture element is formed in each field surrounded by theplural gate electric wirings and the drain electric wirings, said eachpicture element having a counter electrode extending in the samedirection as the drain electric wiring, connected to the common electricwiring corresponding to each picture element, and a picture elementelectrode extending in the same direction as the counter electrodeconnected to the thin film transistor corresponding to each pictureelement. By an electrical voltage applied between said counter electrodeand said picture element electrodes, an electric field is generated thathas a parallel component mainly opposite to said one substrate in theliquid crystal layer. The counter electrode contacts the liquid crystallayer directly.

According to an embodiment of the present invention, the insulator layeris formed on top of the common electric wiring, and the counterelectrode is connected with the common electric wiring through thecontact hole formed by this insulator layer. The insulator layerconsists of a first insulator layer and a second insulator layer, thefirst insulator layer being formed on the gate electric wiring and thecommon electric wiring, and the second insulator layer being formed onthe drain electric wiring and the plural thin film transistors.

Moreover, the source electrode of each thin film transistor is formed onthe first insulator layer and serves as the picture element electrode.Furthermore, the source electrode may be connected to the pictureelement electrode through the contact hole formed by the secondinsulator layer mentioned above. In this case, the picture elementelectrode contacts the liquid crystal layer directly, the counterelectrode. It is preferable that the counter electrode or the pictureelement electrode consists of a conductive oxide film or graphite.

According to another embodiment of the present invention, a drainelectric wiring terminal and a gate electric wiring terminal, in whichthe drain electric wiring and the gate electric wiring are connected tothe drive circuitry, are constructed with the conductive oxide film orthe graphite.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will be understood more clearly from the following detaileddescription with reference to the accompanying drawings, wherein:

FIG. 1 is a sectional view of an active matrix substrate forming anembodiment 1 of the present invention.

FIG. 2 is a plane view of the picture element of FIG. 1, and the A-A′cross section of this figure corresponds to FIG. 1.

FIG. 3 is a sectional view of a conventional active matrix substrate.

FIG. 4 is a plane view of the picture element of FIG. 3, and the B-B′cross section of this figure corresponds to FIG. 3.

FIG. 5 is a sectional view of an active matrix substrate forming anembodiment 2 of the present invention.

FIG. 6 is a plane view of the picture element of FIG. 5, and the C-C′cross section of this figure corresponds to FIG. 5.

FIG. 7 is a sectional view of an active matrix substrate forming anembodiment 3 of the present invention.

FIG. 8 is a plane view of the picture element of FIG. 7, and the D-D′cross section of this figure corresponds to FIG. 7.

FIG. 9 is a sectional view of an active matrix substrate forming anembodiment 4 of the present invention.

FIG. 10 is a plane view of the picture element of FIG. 9, and the E-E′cross section of this figure corresponds to FIG. 9.

FIG. 11 is a sectional view of an active matrix substrate forming anembodiment 5 of the present invention.

FIG. 12 is a plane view of the picture element of FIG. 11, and the F-F′cross section of this figure corresponds to FIG. 11.

FIG. 13 is a sectional view of an active matrix substrate forming anembodiment 6 of the present invention.

FIG. 14 is a plane view of the picture element of FIG. 13, and the G-G′cross section of this figure corresponds to FIG. 13.

FIG. 15 is a sectional view of an active matrix substrate forming anembodiment 7 of the present invention.

FIG. 16 is a plane view of the picture element of FIG. 15, and the H-H′cross section of this figure corresponds to FIG. 15.

FIG. 17 is a sectional view of an active matrix substrate forming anembodiment 8 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A gate electric wiring formed on a transparent insulator substrate(scanning electric wiring) and a metal film serving as a common electricwiring are made of Cr, Al, Ta or alloy thereof. Moreover, in a gateinsulator film, a semi-conductor film, SiN film, SiO film, or a-Si filmmade by the CVD method (Chemical Vapor Deposition method) are used, andfurthermore, N (+) a-Si (phosphorus doped a-Si is used for the contactlayer. These films are processed as described, and the TFT is formed asan active component. Furthermore, as the drain electric wiring (imageelectric wiring) and the source electrode (picture element electrode) ofthe TFT, Cr, Al, Ta or alloy thereof are used.

Furthermore, as a protective insulator film, a SiN film mace by achemical vapor deposition method is used. After forming the protectiveinsulator film, a contact hole is formed for effecting contact betweenthe source electrode and the common electric wiring. Moreover, a contacthole for a terminal of the gate electric wiring, the common electricwiring and the drain electric wiring are formed, and a picture elementelectrode and an counter electrode are formed thereon.

As the picture element electrode and the counter electrode, a conductiveoxide film, such as ITO (Indium Tin Oxide) and graphite, are desirable.These are stable chemically, and so even if the liquid crystal istouched, a good electrical characteristic may be maintained. Moreover,since the terminal for the gate electric wiring, the common electricwiring and the drain wiring are coated with a conductive oxide film, astable contact characteristic may be obtained. Moreover, since thepicture element electrode and the courter electrode of the conductiveoxide film formed on the insulation protective film may apply a directelectric field on the liquid crystal, the electrical voltage loss issmall and the driving voltage for the liquid crystal may be small incomparison with a case wherein the electric field is applied through aconventional insulation protective film. Finally, any danger that thepicture element electrode and the counter electrode of the conductiveoxide film will be deteriorated by the enclosed liquid crystalcomposition is extremely small.

In the conventional liquid crystal display device, an alignment film ofthe liquid crystal is formed, and the thickness of said film is in theorder of 1000 Å, so that any action as a passivation film of thesemiconductor device does not arise, and the degradation of metal filmby the liquid crystal composition cannot be prevented, because there aredefects, such as pinholes, as well. However, the conductive oxide filmis superior because such a degradation does not arise.

As such a conductive oxide film, an ITO (Indium Tin Oxide) film may beused. ITO includes amorphous material ITO and crystalline structure ITO,and in order to reduce the contact resistance of the source electrode,the common electric wiring, the gate electric wiring and the drainelectric wiring, it is desirable to use a crystalline structure ITOfilm. The conductive oxide film made of ITO etc., referred to as atransparent conductive film, is able to transmit a visible light.Although a component of the electric field perpendicular to thesubstrate on the transparent conductive film becomes larger as theapplied electric field usually becomes zero or smaller than zero, whendisplaying a part in black, this part may shade the light too, if theoptics are designed so as to make the polarized light transmissionfactor of the liquid crystal almost zero.

Moreover, it is possible to shade the light with a configuration formedby overlapping metal films on the transparent conductive film. Forexample, the metal source electrode and for common electrode are formedto be overlapped when viewed in a direction vertical to the transparentconductor film and the substrate. In such a configuration, in order tomake the aperture ratio larger, an electrode consisting of the abovemetal films overlapping with the picture element electrode and thecounter electrode in the aperture, is formed to have the same shape asthe picture element electrode and the counter electrode. On thisaccount, a photo lithography process is used for the formation of thepicture element electrode and the counter electrode.

In this case, there is also a system to form the resist pattern byexposing a rear face on the substrate. In particular, the ITO filmsurface is coated with a resist film, a pattern except for the pictureelement aperture is exposed from the surface and also from the rearface, whereby the resist pattern is formed to have the same shape as themetal film in the aperture. By etching, the picture element electrodeand the counter electrode are processed to have a pattern which is thesame as the metal film in the aperture. By this rear face exposureprocess, the electrode width of the picture element electrode and thecounter electrode may be made smaller, and at the same time, it becomespossible to restrain the shading formed by the metal film to a neededminimum size. By forming this metal film with the common electric wiringand the source electrode, the device may be made without adding afurther production process. Moreover, since the electric potential ofthe picture element electrode and the counter electrode becomes the sameas that of the metal film corresponding to the respective electrodeselectrically, no capacitance need be formed. By providing the rear faceexposure in accordance with the present invention, the picture elementelectrode and the counter electrode may be formed to have the same shapeas the metal film in the aperture, thereby, it may be processed withoutconsidering the layout precision of the metal film. Moreover, sinceshading the light at the drain electric wiring and the oppositionelectrode interval next to the drain electric wiring, by forming ashading layer using a metal film similar to the gate electrode so as tooverlap these electrodes as seen in a direction transverse to thesubstrate, the black matrix of the opposite substrate corresponding tothis part can be omitted. The location precision of the active matrixsubstrate and the courter electrode, when they are formed, is aboutseveral to ten μm, and the width of the black matrix needs to bedesigned broadly as several to ten μm. On this account, the apertureratio of the liquid crystal panel is improved by omitting the blackmatrix.

An alignment film is formed on the active matrix substrate providing thepicture element electrode and the counter electrode on top of theprotective insulator film, and next, the opposite substrate is mountedthereto through the use of distance setting beads so as to provide aliquid crystal cell. A predetermined liquid crystal composition isenclosed in said cell, whereby a liquid crystal display device isprovided.

Because the driving voltage of the liquid crystal display device may besmall, the power consumption thereof may be reduced. Moreover, by usingthe active matrix substrate of the present invention, the degree offreedom to select a preferred liquid crystal for a particular thresholddriving voltage may be widened, and so it becomes possible tomanufacture a liquid crystal display device having a fastresponsiveness. Moreover, because the electrical voltage loss is smallcompared with the conventional type device, it becomes possible to makethe spacing between the picture element electrode and the counterelectrodes larger, and so the aperture ratio is improved. Thereby, abright display panel is obtained, and the power consumption of thebacklight may be made small.

In the formation of the picture element electrode and the counterelectrode formed of an ITO film, the terminal is formed by a productionprocess which is the same as ITO film coating, and so the active matrixsubstrate of the present invention may be manufactured with almost thesame number of production processes as usual, with the result that thereis hardly any increase in the manufacturing cost. Moreover, as theelectric field applied to the liquid crystal increases by using theactive matrix substrate of the present invention, it becomes possible toselect a liquid crystal having a larger threshold. That is, it becomespossible to select a liquid crystal, which has a fast responsiveness,and so a liquid crystal display device having a good moving picturecharacteristic and fast response is easily provided.

Moreover, the spacing between the picture element electrode and thecourter electrodes is made larger, and the metal film of the same layeras the gate electrode is used to overlap on the drain electric wiringand the courter electrode next to the drain electric wiring, whereby, ashading layer is formed. With such a construction, the black matrixcorresponding to this part may be omitted, the aperture ratio becomeslarger, a bright display is provided, and the power consumption of thebacklight may be small.

Based on the drawings, various embodiments of the present invention willnow be explained more specifically.

[Embodiment 1]

A sectional view of a picture element of an active matrix substrate inaccordance with the present invention is shown in FIG. 1, and a planeview thereof is shown in FIG. 2.

A Cr film having a thickness of 200 nm is formed on a transparentsubstrate 1 by a sputtering method. Subsequently, the gate electricwiring 2 and the common electric wiring 3 are formed thereon by using aphoto lithography method. Then, the substrate 1 on which the gateelectric wiring 2 and the common electric wiring 3 are formed isprovided in a plasma CVD device with a SiN film of 350 nm as the gatinginsulator film 4, a a-si film of 200 nm as a semi-conductor film 5, anda n(+)a-si film of 30 nm as a contact layer 6. As the materials gas, amixture gas of SiH4, NH3, H for forming a SiN film, a mixture gas ofSiH4 and H2 for forming a a-Si memblem, and a mixture gas of SiH4 and H2with the further addition of PH3 for forming a n(+)a-si memblem areused. Then, n(+)a-si and a-si are formed like islands so as to form aTFT by using a photo lithography method.

Next, a Cr film is formed to be a memblem having a thickness of 200 nmby a sputtering method, and a drain electric wiring 7 and a sourceelectrode 8 are formed by using a photo lithography method. The n(+)a-sifilm of the channel is removed by dry etching afterwards. A protectiveinsulator film 9 (SiN) is formed by a plasma chemical vapor depositionmethod thereon. Using a photo lithography method again, in the SiN gateinsulator film 4 and the protective insulator film 9, respective contactholes 10 are formed to reach the source electrode 8 and the commonelectric wiring 3, the gate electric wiring terminal, and a contact holeof the drain electric wiring terminal are formed.

A crystalline ITO film is formed to have a thickness of 200 nm at asubstrate temperature of 220 degrees by a DC magnetron sputteringmethod. The ITO film is processed by a photo lithography method to formthe picture element electrode 11 and the counter electrode 12, and thedrain electric wiring terminal, the gate electric wiring terminal andthe drain electric wiring terminal are formed. The picture elementelectrode 11 and the counter electrode 12 formed by this process arerespectively connected with the source electrode 8 and the commonelectric wiring 3 electrically.

An alignment film of the liquid crystal (polyimide film) which alignsmolecules of the liquid crystal in a predetermined direction is formedon the active matrix substrate already formed, which substrate is thenmounted on the opposite substrate through distance setting beads, andthe liquid crystal composition is enclosed therein, whereby the liquidcrystal display device is obtained.

The liquid crystal driving voltage of the above liquid crystal displaydevice may be reduced 20% or more, compared with one using an activematrix substrate having a construction shown in FIG. 3 and FIG. 4.Moreover, because both the picture element electrode 11 and the counterelectrode 12 are formed with an ITO film, it has a good effect in thatthere is hardly any degradation caused by the liquid crystal compositionetc.

[Embodiment 2]

A sectional view of a picture element of the active matrix substrate ofthe present invention is shown in FIG. 5, and a plane view thereof isshown in FIG. 6.

The gate electrode, the common electrode, the drain electrode and thesource electrode are formed with a Cr—Mo alloying film in thisembodiment. In order to control the stress of the Cr—Mo alloying film(film thickness 200 nm) formed by a sputtering method on a transparentsubstrate 1 to a low level, the Mo is kept at 30 to 50 weight %.Moreover, the Cr—Mo alloying may suppress the contact resistance withthe ITO film formed later to a low level. Subsequently, the gateelectric wiring 2 and the common electric wiring 3 is formed by using aphoto lithography method. Here, the common electric wiring of theaperture is processed into a shape to overlap with the counter electrode12 formed later. Furthermore, in the same way as the embodiment 1, a SiNfilm forms the gate insulator film 4, a a-Si film forms thesemi-conductor film 5, and a n(+)a-Si film forms the contact layer 6.

The Cr—Mo film is formed so as to have a thickness of 200 nm by asputtering method, and the drain electric wiring 7 and the sourceelectrode 8 are formed by using a photo lithography method. Here, thesource electrode 8 is processed to overlap with the picture elementelectrode 11 formed later. The N(+)a-Si film is removed by a dry etchingmethod afterwards, and the a-Si film is processed like an island using aphoto lithography method, whereby the TFT is formed. The protectiveinsulator film 9 (SIN) is formed thereon by a plasma chemical vapordeposition method. The contact holes 10 to reach the source electrodeand the common electric wiring are respectively provided in the gateinsulator film 4 and the SiN of the protective insulator film 9, andthen, the drain electric wiring terminal, the gate electric wiringterminal and the contact hole of the drain electric wiring terminal areformed.

The ITO film is formed to have a thickness of 200 nm by the method asembodiment 1, and a coating film of picture element electrode 11,counter electrode 12, a drain electric wiring terminal, a gate electricwiring terminal and a drain electric wiring terminal are formed using aphoto lithography method. The picture element electrode 11 and thecounter electrode 12 formed by this process are respectively connectedto the source electrode 8 and common electric wiring 3 electrically.

An alignment film is formed on the active matrix substrate mentionedabove, and the substrate is then mounted on the opposite substratethrough distance setting beads, and a liquid crystal composition isenclosed therein to form the liquid crystal display device. The liquidcrystal driving voltage of the above liquid crystal display device maybe reduced by 20% or more, compared with one using an active matrixsubstrate having a construction shown in FIG. 3 and FIG. 4.

[Embodiment 3]

A sectional view of the picture element of the active matrix substrateof the present invention is shown in FIG. 7, and a plane view thereof isshown in FIG. 8.

The gate electric wiring 2, the common electric wiring 3, the gateinsulator film 4, the TFT element, the drain electric wiring 7, and thesource electrode 8 are formed in the same way as in embodiment 1. Theprotective insulator film 9 (SIN) is formed by plasma chemical vapordeposition thereon. Furthermore, the gate insulator film 4, the contacthole 10 to connect to the source electrode 8 and the common electricwiring 3 on the SiN film of the protective insulator film 9, and thecontact hole of the drain electric wiring terminal, the gate electricwiring terminal and the drain electric wiring terminal are formed by aphoto lithography method.

The ITO film is formed to have a thickness of 200 nm in the same way asin embodiment 1. Then, the picture element electrode 11, the counterelectrode 12, the coating film of the drain electric wiring terminal,the gate electric wiring terminal and the drain electric wiring terminalare formed by a photo lithography method. Here, the apertures of thepicture element electrode 11 and counter electrode 12 are respectivelyprocessed to have the same shape as those of the source electrode 8 andthe common electric wiring 3 by exposing the substrate 1 from the rearface thereof. Thereby, since the mask matching precision does not needto be considered with respect to the source electrode 8 and the commonelectric wiring 3, respectively, relative to the picture elementelectrode 11 and the counter electrode 12, the width of the sourceelectrode 8 and common electric wiring 3 in the aperture may be formedto be smaller and the aperture ratio may be increased.

An alignment film is formed on the active matrix substrate mentionedabove, which substrate is then mounted on the opposite substrate throughdistance setting beads, and the liquid crystal composition is enclosedin it, whereby the liquid crystal display device is obtained. Such aliquid crystal display device as described above has the advantage thatthe liquid crystal driving voltage is small and a bright image is ableto be obtained.

[Embodiment 4]

A sectional view of the picture element of the active matrix substrateof the present invention is shown in FIG. 9, and a plane view thereof isshown in FIG. 10.

The gate electric wiring 2, the common electric wiring 3, the gateinsulator film 4, the semi-conductor layer 5, the contact layer 6, thedrain electric wiring 7 and the source electrode 8 are formed ontransparent substrate 1 in the same way as in embodiment 1. Theprotective insulator film 9, the contact hole 10 and the counterelectrode 12 also are formed using the same method as embodiment 1.According to the above-mentioned process, the courter electrode 12 andthe common electric wiring 3 are connected to each other electrically.

An alignment film is formed on the active matrix substrate mentionedabove, which substrate is then mounted on the opposite substrate throughdistance setting beads, and the liquid crystal composition is enclosedin it, whereby the liquid crystal display device is obtained. The liquidcrystal driving voltage of the above liquid crystal display device maybe reduced by 10% or more, compared with one using the active matrixsubstrate having a construction shown in FIG. 3 and FIG. 4.

In this embodiment, only the counter electrode is constituted to touchthe liquid crystal layer directly, and the source electrode is formed ofmetal, so that it serves as the picture element electrode. By theconstruction employed in this embodiment, there are a smaller number ofthrough holes.

[Embodiment 5]

A sectional view of the picture element of the active matrix substrateof the present invention is shown in FIG. 11, and a plane view thereofis shown in FIG. 12.

The gate electric wiring 2, the common electric wiring 3, the gateinsulator film 4, the semi-conductor layer 5, the contact layer 6, thedrain electric wiring 7 and the source electrode 8 are formed ontransparent substrate 1 in the same way as in embodiment 1. Theprotective insulator film 9, the contact hole 10 and the pictureelectrode 11 also are formed with the same method as embodiment 1.According to the above-mentioned process, the counter electrode 12 andthe common electric wiring 3 are connected to each other electrically.

An alignment film is formed on the active matrix substrate mentionedabove, which substrate is then mounted on the opposite substrate throughdistance setting beads, and the liquid crystal composition is enclosedin it, whereby the liquid crystal display device is obtained. The liquidcrystal driving voltage of the above liquid crystal display device maybe reduced by 10% or more, compared with one using the active matrixsubstrate having a construction shown in FIG. 3 and FIG. 4.

In this embodiment, the counter electrode is formed by the same processas the common electrode. By the construction employed in thisembodiment, there are a smaller number of through holes.

[Embodiment 6]

A sectional view of a typical picture element of the active matrixsubstrate of the present invention is shown in FIG. 13, and a plane viewthereof is shown in FIG. 14.

The gate electric wiring 2 is formed on transparent substrate 1 with thesame method as embodiment 1. Here, at same time, the shading layer 13 isformed to overlap with the drain electric wiring 7 and the counterelectrode 12 formed later. Then, the common electric wiring 3, the gateinsulator film 4, the semi-conductor layer 5, the contact layer 6, thedrain electric wiring 7 and the source electrode 8 are formed using thesame method as embodiment 1. The protective insulator film 9, thecontact hole 10 and the counter electrode 12 also are formed using thesame method as embodiment 1. According to the above-mentioned process,the courter electrode 12 and the common electric wiring 3 are connectedto each other electrically.

An alignment film is formed on the active matrix substrate mentionedabove, which substrate is then mounted the opposite substrate throughdistance setting beads, and the liquid crystal composition is enclosedin it, whereby the liquid crystal display device is obtained. The liquidcrystal driving voltage of the above liquid crystal display device maybe reduced by 10% or more, compared with one using the active matrixsubstrate having a construction shown in FIG. 3 and FIG. 4. Moreover, byusing the light shading layer 13, the black matrix of the oppositesubstrate in this part may be omitted, thereby resulting in an improvedaperture ratio.

[Embodiment 7]

A sectional view of a typical picture element of the active matrixsubstrate of the present invention is shown in FIG. 15, and a plane viewthereof is shown in FIG. 16.

The gate electric wiring 2, the common electric wiring 3, the gateinsulator film 4, the TFT, the drain electric wiring 7 and the sourceelectrode 8 are formed in the same way as in embodiment 1. Theprotective insulator film 9 (SIN) is formed by plasma chemical vapordeposition thereon. Furthermore, the gate insulator film 4, the contacthole 10 to connect to the source electrode 8 and the common electricwiring 3 on the SiN film of the protective insulator film 9, and thecontact hole of the drain electric wiring terminal, the gate electricwiring terminal and the drain electric wiring terminal are formed by aphoto lithography method.

A graphite film is formed as a memblem having a thickness of 200 nm by asputtering method. Then, the picture element electrode 11, the counterelectrode 12, and the coating film of the drain electric wiringterminal, the gate electric wiring terminal, and the drain electricwiring terminal are formed by processing the graphite film using a photolithography method.

An alignment film is formed on the active matrix substrate mentionedabove, which substrate is then mounted on the opposite substrate througha distance setting piece, and the liquid crystal composition is enclosedin it, whereby the liquid crystal display device is obtained. Such aliquid crystal display device has the advantage that the liquid crystaldriving voltage is small, and a bright image is able to be obtained.

[Embodiment 8]

An active matrix substrate, shown in plane view in FIG. 17, is formed byusing the same method as embodiment 3. In the embodiment 3, as shown inFIG. 8, two picture element electrodes 11 and three counter electrodes12 are provided in one picture element; however, in this embodiment 8,there are one picture element electrode 11 and two counter electrodes 12in one picture element. Thereby, in this embodiment, a higher apertureratio may be provided compared with that in the embodiment 3.

An alignment film is formed on the active matrix substrate mentionedabove, which substrate is then mounted on the opposite substrate througha distance setting piece, and the liquid crystal composition is enclosedin it, whereby the liquid crystal display device is obtained. Such aliquid crystal display device as described above has the advantage thatthe liquid crystal driving voltage is small and a bright image is ableto be obtained.

According to the present invention, the driving voltage of the liquidcrystal display device using an in-plane-switching system may be reducedas mentioned above. Moreover, it becomes possible to use a liquidcrystal having higher threshold driving voltage, with the result that aliquid crystal display device having fast responsiveness may beprovided.

What is claimed is:
 1. A liquid crystal display device comprising a pairof substrates, and a liquid crystal layer supported between said pair ofsubstrates, said liquid crystal display device further comprising: aplurality of gate electric wirings provided on one of said pair ofsubstrates; a plurality of drain electric wirings respectivelyintersecting with said plurality of gate electric wirings in a matrixconfiguration; a plurality of thin film transistors formed on respectivepoints of said gate electric wirings and said drain electric wirings; aplurality of common electric wirings extending in the same direction assaid gate electric wirings; a plurality of picture elements, at leastone of said picture elements being respectively surrounded by said gateelectric wirings and said drain electric wirings; and a plurality ofcounter electrodes connected to said common electric wirings andextending in the same direction as said drain electric wirings, aplurality of picture element electrodes made of at least one ofconductive oxide and graphite being connected to said thin filmtransistors and extending in the same direction as said drain electricwirings; wherein an electric field having a component parallel to one ofsaid pair of substrates is produced in said liquid crystal layer by anelectric voltage applied between said counter electrodes and saidpicture element electrodes, and said respective picture elementelectrodes are separated from said liquid crystal layer by at least analignment film which aligns molecules of said liquid crystal layer in apredetermined direction.
 2. A liquid crystal display device as definedin claim 1, further comprising an insulator layer formed on said commonelectric wirings, wherein said picture element electrodes arerespectively connected to said thin film transistors through a contracthole formed in said insulator layer formed on said thin filmtransistors.
 3. A liquid crystal display device as defined in claim 1,wherein each source electrode serves as a picture element electrode. 4.A liquid crystal display device as defined in claim 3, wherein saidcounter electrodes are constructed of at least one of a conductive oxidefilm and graphite.
 5. A liquid crystal display device as defined inclaim 1, wherein a drain electric wiring terminal and a gate electricwiring terminal, in which said plural drain electric wirings and saidplural gate electric wirings are connected to a drive circuitry, areconstructed of at least one of a conductive oxide film and graphite. 6.A liquid crystal display device comprising a pair of substrates, and aliquid crystal layer supported between said pair of substrates, saidliquid crystal display device further comprising: a plurality of gateelectric wirings provided on one of said pair of substrates; a pluralityof drain electric wirings respectively intersecting with said pluralityof gate electric wirings in a matrix configuration; a plurality of thinfilm transistors formed on respective intersecting points of said gateelectric wirings and said drain electric wirings; a plurality of commonelectric wirings extending in the same direction as said gate electricwirings; a plurality of picture elements, at least one of said pictureelements being respectively surrounded by said gate electric wirings andsaid drain electric wirings; and a plurality of counter electrodesconnected to said common electric wirings and extending in the samedirection as said drain electric wirings, a plurality of said pictureelement electrodes being connected to said thin film transistors andextending in the same direction as a counter electrode corresponding tosaid respective picture elements; wherein said gate electric wirings andsaid common electric wirings are formed on the same layer and a firstinsulator layer is formed on said gate electric wirings and said commonelectric wirings, said drain electric wirings are formed on said firstinsulator layer, a second insulator layer is formed on said drainelectric wirings, said counter electrodes are formed on said secondinsulator layer, said counter electrodes are connected to saidcorresponding common electric wirings through a contact hole formed insaid first and second insulator layers, and said counter electrodes areseparated from said liquid crystal layer at least by an alignment filmwhich aligns molecules of said liquid crystal layer in a predetermineddirection.
 7. A liquid crystal display device comprising a pair ofsubstrates, and a liquid crystal layer supported between said pair ofsubstrates, said liquid crystal display device further comprising: aplurality of gate electric wirings provided on one of said pair ofsubstrates; a plurality of drain electric wirings respectivelyintersecting with said plurality of gate electric wirings in a matrixconfiguration; a plurality of thin film transistors formed on respectivepoints of said gate electric wirings and said drain electric wirings; aplurality of common electric wirings extending in the same direction assaid gate electric wirings; a plurality of picture elements, at leastone of said picture elements being respectively surrounded by said gateelectric wirings and said drain electric wirings; and a plurality ofcounter electrodes connected to said common electric wirings andextending in the same direction as said drain electric wirings, aplurality of picture element electrodes made of at least one ofconductive oxide and graphite being connected to said thin filmtransistors and extending in the same direction as said drain electricwirings; wherein an electric field having a component parallel to one ofsaid pair of substrates is produced in said liquid crystal layer by anelectric voltage applied between said counter electrodes and saidpicture element electrodes, and said respective picture elementelectrodes are in contact with said liquid crystal layer directly.
 8. Aliquid crystal display device as defined in claim 7, further comprisingan insulator layer formed on said common electric wirings, wherein saidpicture element electrodes are respectively connected to said thin filmtransistors through a contract hole formed in said insulator layerformed on said thin film transistors.
 9. A liquid crystal display deviceas defined in claim 7, wherein each source electrode serves as a pictureelement electrode.
 10. A liquid crystal display device as defined inclaim 9, wherein said counter electrodes are constructed of at least oneof a conductive oxide film and graphite.
 11. A liquid crystal displaydevice as defined in claim 7, wherein a drain electric wiring terminaland a gate electric wiring terminal, in which said plural drain electricwirings and said plural gate electric wirings are connected to a drivecircuitry, are constructed of at least one of a conductive oxide filmand graphite.